/*
 * Copyright (C) 2016 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.google.common.graph;

import static com.google.common.base.Preconditions.checkNotNull;
import static com.google.common.base.Preconditions.checkState;
import static java.util.Objects.requireNonNull;

import java.util.Collections;
import java.util.Map;
import java.util.Set;
import javax.annotation.CheckForNull;

/**
 * A base implementation of {@link NetworkConnections} for undirected networks.
 *
 * @param <N> Node parameter type
 * @param <E> Edge parameter type
 * @author James Sexton
 */
@ElementTypesAreNonnullByDefault
abstract class AbstractUndirectedNetworkConnections<N, E> implements NetworkConnections<N, E>
{
    /**
     * Keys are edges incident to the origin node, values are the node at the other end.
     */
    final Map<E, N> incidentEdgeMap;

    AbstractUndirectedNetworkConnections(Map<E, N> incidentEdgeMap)
    {
        this.incidentEdgeMap = checkNotNull(incidentEdgeMap);
    }

    @Override
    public Set<N> predecessors()
    {
        return adjacentNodes();
    }

    @Override
    public Set<N> successors()
    {
        return adjacentNodes();
    }

    @Override
    public Set<E> incidentEdges()
    {
        return Collections.unmodifiableSet(incidentEdgeMap.keySet());
    }

    @Override
    public Set<E> inEdges()
    {
        return incidentEdges();
    }

    @Override
    public Set<E> outEdges()
    {
        return incidentEdges();
    }

    @Override
    public N adjacentNode(E edge)
    {
        // We're relying on callers to call this method only with an edge that's in the graph.
        return requireNonNull(incidentEdgeMap.get(edge));
    }

    @Override
    @CheckForNull
    public N removeInEdge(E edge, boolean isSelfLoop)
    {
        if (!isSelfLoop)
        {
            return removeOutEdge(edge);
        }
        return null;
    }

    @Override
    public N removeOutEdge(E edge)
    {
        N previousNode = incidentEdgeMap.remove(edge);
        // We're relying on callers to call this method only with an edge that's in the graph.
        return requireNonNull(previousNode);
    }

    @Override
    public void addInEdge(E edge, N node, boolean isSelfLoop)
    {
        if (!isSelfLoop)
        {
            addOutEdge(edge, node);
        }
    }

    @Override
    public void addOutEdge(E edge, N node)
    {
        N previousNode = incidentEdgeMap.put(edge, node);
        checkState(previousNode == null);
    }
}
